The present invention generally relates to magnetic tapes having multiple tracks which are recorded with digital signals and recording apparatus therefor, and more particularly to a magnetic tape which is recorded with digital signals which are reproduced from a master tape, where the master tape is recorded with the digital signals in an optimum state on one or a plurality of forward recording tracks which are scanned when the master tape travels in a forward direction during a normal reproducing mode and on one or a plurality of reverse recording tracks which are scanned when the master tape travels in a reverse direction during the normal reproducing mode, and a recording apparatus therefor. The magnetic tape according to the present invention is recorded with the digital signals which are reproduced from both the forward and reverse tracks on the master tape as the master tape travels in one direction, so that the forward and reverse tracks are simultaneously formed on the magnetic tape.
When recording analog information signals such as audio and video signals as digital signals, the analog information signals are subjected to a digital pulse modulation so as to obtain a digital data sequence. A synchronizing signal, error detecting codes, error correcting codes, and the like are added to this digital data sequence, to constitute a digital signal of one frame. The digital signals are recorded onto a magnetic tape by stationary heads in terms of frames. Conventionally, when carrying out the recording of the digital signals in the manner described above, one or a plurality of forward recording tracks are formed as the magnetic tape (particularly a cassette tape) travels in one direction. When the forward recording tracks are formed up to one end of the magnetic tape, the magnetic tape is turned over in order to form one or a plurality of reverse recording tracks as the magnetic tape travels in the above one direction. The reverse recording tracks are formed up to the other end of the magnetic tape. Further, the reverse recording tracks are formed at locations which are different from the locations of the forward recording tracks. On the other hand, when the above pre-recorded magnetic tape is played, the recorded digital signals are reproduced from the forward recording tracks or the reverse recording tracks, while the magnetic tape travels similarly as in the case during the recording.
Conventionally, when producing the pre-recorded magnetic tape (such as a pre-recorded music cassette tape), a master tape is first prepared. Desired digital signals are then recorded in an optimum state on the forward recording tracks and the reverse recording tracks on this master tape. In a high-speed reproducing apparatus, the master tape is driven to travel in one direction at a tape speed which is eight times the tape speed which is employed during the normal (original) recording and reproducing modes, for example. Thus, the digital signals are simultaneously reproduced from n forward recording tracks (n is a natural number greater than or equal to one) and n reverse recording tracks, in the high-speed reproducing apparatus. The digital signals which are simultaneously reproduced in parallel from 2n tracks, are supplied to a high-speed recording apparatus. In the high-speed recording apparatus, a magnetic tape (slave tape) is driven to travel in one direction at a high tape speed which is identical to the high tape speed employed in the high-speed reproducing apparatus, and the reproduced digital signals from the high-speed reproducing apparatus are simultaneously recorded onto n forward recording tracks and n reverse recording tracks on the slave tape. The slave tape can be recorded within a short period of time, because the n forward recording tracks and the n reverse recording tracks are simultaneously formed on the slave tape as the slave tape travels in one direction. Such a recording technique was advantageous, since it eliminated the need to drive the master tape in both the forward and reverse directions in order to reproduce the digital signals from the forward and reverse recording tracks, and moreover, it eliminated the need to drive the slave tape in both the forward and reverse directions in order to record the digital signals which are reproduced from the master tape. Accordingly, the production efficiency was improved by employing such a recording technique.
However, when producing the slave tape according to the above described recording technique, either the forward recording tracks or the reverse recording tracks will be formed and recorded as the slave tape travels in a direction which is opposite to the direction in which the tape travels when those tracks are scanned upon reproduction. As a result, the waveforms of the digital signals which are reproduced from the forward recording tracks, become different from the waveforms of the digital signals which are reproduced from the reverse recording tracks. Suppose that the digital signals which are reproduced from the recording tracks as the tape travels in a direction which is identical to the direction in which the tape traveled when the digital signals were recorded on the same recording tracks, have solitary waveforms. In the solitary waveform, a first time width between a peak level reproducing time when the peak level is obtained and a reproducing time when a first zero which is immediately prior to this peak level reproducing time is obtained, is generally shorter compared to a second time width between the peak level reproducing time and a reproducing time when a first zero which is immediately subsequent to the peak level reproducing time is obtained, as in the case during the recording. In the present specification, a term "assymmetry of zeros" will be used to indicate a case where the above first and second time widths are different.
Various reasons for such assymmetry of zeros in the solitary waveform, have been reported. For example, D. F. Eldridge, "Magnetic recording and reproduction og pulses", IRE trans. Audio, pp. 47-52, Aug. 8, 1960, discloses the effects of magnetization components in a vertical direction to a magnetic surface. N. Curland and D. E. Speliotis, "An iterative hysteretic model for digital magnetic recording", IEEE Trans. Magn., vol. MAG-7, no. 3, pp. 538-543, 1971, discloses the effects of assymmetry of the transition zone. Further, A. V. Davies, "The influence of some head and coating properties on pulse resolution in NRZ digital recording", In Int. Conf. Digital Recording, London, pp. 68-71, 1964, for example, discloses the effects of time lag in an electrical circuit due to eddy current and head inductance.
The digital signals which are reproduced from the magnetic tape, are supplied to an equalizer circuit in a reproducing system of a recording and reproducing apparatus. For example, the equalizer circuit compensates for a high-frequency component which was attenuated during the process of the magnetic recording and reproduction, and converts the reproduced digital signals into a predetermined signal format. The converted signals from the equalizer circuit are supplied to an automatic threshold control circuit which restores the converted signals into the original binary coded digital signals, under the control of a clock signal. Thus, by taking into consideration the recording and reproducing characteristics of the recording and reproducing apparatus, the equalizer circuit in the reproducing system of the recording and reproducing apparatus is pre-adjusted so that optimum solitary waveforms which have the same assymmetry of zeros as the solitary waveforms upon recording, are reproduced from the recording tracks as the magnetic tape travels in a direction which is the same as the direction in which the magnetic tape traveled when the same recording tracks were recorded.
However, the digital signals may be reproduced from the recording tracks as the magnetic tape travels in a direction which is opposite to the direction in which the magnetic tape traveled when the same recording tracks were recorded. In this case, the solitary waveforms which are reproduced from the recording tracks, do not have the same assymmetry of zeros as the solitary waveforms upon recording. In the solitary waveform obtained in this case, the assymmetry of zeros is such that a first time width between a peak level reproducing time when the peak level is obtained and a reproducing time when a first zero which is immediately prior to this peak level reproducing time is obtained, is longer compared to a second time width between the peak level reproducing time and a reproducing time when a first zero which is immediately subsequent to the peak level reproducing time is obtained.
Accordingly, when the conventional recording and reproducing apparatus played a pre-recorded magnetic tape which had been recorded with the high-speed recording technique described before, the equalizer circuit could not carry out an optimum waveform equalization while the digital signals were being reproduced from the recording tracks as the magnetic tape traveled in a direction which was opposite to the direction in which the magnetic tape traveled when the same recording tracks were recorded. As a result, the error rate of the reproduced digital signals was unsatisfactory. Moreover, when the original analog information signals were audio signals, there were problems in that discontinuities were introduced in the reproduced sounds, and noise were generated in the reproduced sounds.